In a diesel engine, fuel injected into a combustion chamber by a fuel injector is compressed and ignited after the elapse of a predetermined time (ignition delay) from injection. To improve output performance and emission performance of diesel engines, control devices are widely used that control the engine control mode for the injection timing and the injection amount in fuel injection while taking the ignition delay into account.
In a diesel engine, the lower the cetane number of fuel used, the longer the ignition delay becomes. Thus, even if the engine control execution mode is set before shipment of a diesel engine, supposing that fuel having a standard cetane number will be used, the ignition timing of fuel will be delayed and the state of combustion will be deteriorated if fuel having a relatively low cetane number such as winter fuel is supplied to the fuel tank. Depending on the case, misfiring occurs.
To suppress the occurrence of such inconvenience, it is desirable to correct the engine control execution mode based on the actual cetane number of fuel to be injected into a combustion chamber. To perform such a correction in a favorable manner, it is necessary to correctly estimate the cetane number of fuel.
Conventionally, a device has been proposed in Patent Literature 1 that injects a small amount of fuel from a fuel injector and estimates a cetane number of the fuel based on engine torque generated with fuel injection. In the device disclosed in this Patent Literature 1, the cetane number of the fuel is estimated based on the relationship between the fuel injection amount and the output torque, which have been individually detected, focusing on the fact that the relationship between fuel injection amount and output torque of the diesel engine changes according to the cetane number.